High specific surface area alpha-Fe2O3 nanostructures as high performance electrode material for supercapacitors

Porous alpha-Fe2O3 nanostructures have been synthesized by a simple sol-gel route. The alpha-Fe2O3 nanostructures are poorly crystalline and porous with BET surface area of 386 m(2) g(-1). The high discharge capacitance of alpha-Fe2O3 electrodes is 300 F g(-1) when the electrodes are cycled in 0.5 M Na2SO3 at a current density of 1 A g(-1). The capacitance retention after 1000 cycles is about 73% of the initial capacitance at a current density of 2 A g(-1). The high discharge capacitance of alpha-Fe2O3 in comparison with the literature reports are attributed to high surface area and porosity of the iron oxide prepared in the present study. As the iron oxides are inexpensive, the capacity of alpha-Fe2O3 is expected to be of potential use for supercapacitor application. (C) 2014 Elsevier B.V. All rights reserved.

Solution Processed Cu2CoSnS4 Thin Films for Photovoltaic Applications

Earth abundant alternative chalcopyrite Cu2CoSnS4 (CCTS) thin films were deposited by a facile sol-gel process onto larger substrates. Temperature dependence of the process control of deposition and desired phase formations was studied in detail. Films were analyzed for complete transformation from amorphous to polycrystalline, with textured structures for stannite phase, as reflected from the X-ray diffraction and with nearly stoichiometric compositions of Cu:Co:Sn:S = 2:0:1:0:1:0:4:0 from EDAX analysis. Morphological investigations revealed that the CCTS films with larger grains, on the order of its thickness, were synthesized at higher temperature of 500 degrees C. The optimal band gap for application in photovoltaics was estimated to be 1.4 eV. Devices with SLG/CCTS/Al geometry were fabricated for real time demonstration of photoconductivity under A.M 1.5 G solar and 1064 rim infrared laser illuminations. A photodetector showed one order current amplification from similar to 1.9 X 10(-6) A in the dark to 2.2 x 10(-5) A and 9.8 X 10(-6) A under A.M 1.5 G illumination and 50 mW cm(-2) IR laser, respectively. Detector sensitivity, responsivity, external quantum efficiency, and gain were estimated as 4.2, 0.12 A/W, 14.74% and 14.77%, respectively, at 50 mW cm(-2) laser illuminations. An ON and OFF ratio of 2.5 proved that CCTS can be considered as a potential absorber in low cost photovoltaics applications.

Co-existence of tetragonal and monoclinic phases and multiferroic properties for x <= 0.30 in the (1-x)Pb(Zr0.52Ti0.48)O-3-(x)BiFeO3 system

Compositions with x <= 0.30 in the system (1- x)Pb(Zro(0.52)Ti(0.48))O-3-(x)BiFeO3 were synthesized by sol-gel method. Rietveld analysis of X-ray diffraction data reveals tetragonal structure (P4mm) for x <= 0.05 and monoclinic (Cm) phase along with the existence of tetragonal phase for 0.10 <= x <= 0.25 and monoclinic phase for x = 0.30. Transformation of E(2TO) and E + B1 vibrational modes in the range 210-250 cm(-1) (present for x <= 0.25) into A' + A `' modes at similar to 236 cm(-1) for x = 0.30, and occurrence of new vibrational modes A' and A `' in Raman spectra for x >= 0.10 unambiguously support the presence of monoclinic phase. Occurrence of remnant polarisation and enhanced magnetization with concentration of BiFeO3 indicates superior multiferroic properties. Variation of magneto-capacitance with applied magnetic field is a strong evidence of magneto-electric multiferroic coupling in these materials. (C) 2014 Elsevier B.V. All rights reserved.

Effect of film thickness and annealing on optical properties of TiO2 thin films and electrical characterization of MOS capacitors

Titanium dioxide (TiO2) thin films were deposited on glass and silicon (100) substrates by the sol-gel method. The influence of film thickness and annealing temperature on optical transmittance/reflectance of TiO2 films was studied. TiO2 films were used to fabricate metal-oxide-semiconductor capacitors. The capacitance-voltage (C-V), dissipation-voltage (D-V) and current-voltage (I-V) characteristics were studied at different annealing temperatures and the dielectric constant, current density and resistivity were estimated. The loss tangent (dissipation) increased with increase of annealing temperature.

Polymorphic phase transition among the titania crystal structures using a solution-based approach: from precursor chemistry to nucleation process

Nanocrystalline titania are a robust candidate for various functional applications owing to its non-toxicity, cheap availability, ease of preparation and exceptional photochemical as well as thermal stability. The uniqueness in each lattice structure of titania leads to multifaceted physico-chemical and opto-electronic properties, which yield different functionalities and thus influence their performances in various green energy applications. The high temperature treatment for crystallizing titania triggers inevitable particle growth and the destruction of delicate nanostructural features. Thus, the preparation of crystalline titania with tunable phase/particle size/morphology at low to moderate temperatures using a solution-based approach has paved the way for further exciting areas of research. In this focused review, titania synthesis from hydrothermal/solvothermal method, conventional sol-gel method and sol-gel-assisted method via ultrasonication, photoillumination and ILs, thermolysis and microemulsion routes are discussed. These wet chemical methods have broader visibility, since multiple reaction parameters, such as precursor chemistry, surfactants, chelating agents, solvents, mineralizer, pH of the solution, aging time, reaction temperature/time, inorganic electrolytes, can be easily manipulated to tune the final physical structure. This review sheds light on the stabilization/phase transformation pathways of titania polymorphs like anatase, rutile, brookite and TiO2(B) under a variety of reaction conditions. The driving force for crystallization arising from complex species in solution coupled with pH of the solution and ion species facilitating the orientation of octahedral resulting in a crystalline phase are reviewed in detail. In addition to titanium halide/alkoxide, the nucleation of titania from other precursors like peroxo and layered titanates are also discussed. The nonaqueous route and ball milling-induced titania transformation is briefly outlined; moreover, the lacunae in understanding the concepts and future prospects in this exciting field are suggested.

Optical and structural properties of highly porous shell structured Fe doped TiO2 thin films

TiO2 thin films with 0.2 wt%, 0.4 wt%, 0.6 wt%, and 0.8 wt% Fe were prepared on glass and silicon substrates using sol-gel spin coating technique. The optical cut-off points are increasingly red-shifted and the absorption edge is shifted over the higher wavelength region with Fe content increasing. As Fe content increases, the optical band gap decreases from 3.03 to 2.48 eV whereas the tail width increases from 0.26 to 1.43 eV. The X-ray diffraction (XRD) patterns for doped films at 0.2 wt% and 0.8 wt% Fe reveal no characteristic peaks, indicating that the film is amorphous whereas undoped TiO2 exhibits (101) orientation with anatase phase. Thin films of higher Fe content exhibit a homogeneous, uniform, and nano-structured highly porous shell morphology.

Effect of Sm3+ on dielectric and magnetic properties of Y3Fe5O12 nanoparticles

The Sm3+ doped Y3-xSmxFe5O12 (x = 0-3) nanopowders were prepared using modified sol-gel route. The crystalline structure and morphology was confirmed by X-ray diffraction and atomic force microscopy. The nanopowders were sintered at 950 degrees C/90 min using microwave sintering method. The lattice parameters and density of the samples were increased with an increase of Sm3+ concentration. The room temperature dielectric (epsilon' and epsilon `') and magnetic (mu' and mu `') properties were measured in the frequency range up to 20 GHz. The room temperature magnetization studies were carried out using Vibrating sample magnetometer using filed of 1.5 T. Results of VSM show that the saturation and remnant magnetization of Y3-xSmxFe5O12 (0-3) decreases on increasing the Sm concentration (x). The low values of magnetic (mu' and mu `') properties makes them a good candidates for microwave devices, which can be operated in the high frequency range.

Domain size correlated magnetic properties and electrical impedance of size dependent nickel ferrite nanoparticles

We report here the investigations on the size dependent variation of magnetic properties of nickel ferrite nanoparticles. Nickel ferrite nanoparticles of different sizes (14 to 22 nm) were prepared by the sol-gel route at different annealing temperatures. They are characterized by TGA-DTA, XRD, SEM, TEM and Raman spectroscopy techniques for the confirmation of the temperature of phase formation, thermal stability, crystallinity, morphology and structural status of the nickel ferrite nanoparticles. The magnetization studies revealed that the saturation magnetization (M-s), retentivity (M-r) increase, while coercivity (H-c) and anisotropy (K-eff) decrease as the particle size increases. The observed value of M-s is found to be relatively higher for a particle size of 22 nm. In addition, we have estimated the magnetic domain size using magnetic data and correlated to the average particle size. The calculated magnetic domain size is closely matching with the particle size estimated from XRD. Impedance spectroscopy was employed to study the samples in an equivalent circuit to understand their transport phenomena. It shows that nickel ferrite nanoparticles exhibit a non-Debye behavior with increasing particle size due to the influence of increasing disorders, surface effects, grain size and grain boundaries, etc. (C) 2015 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.

Size Dependent Magnetic Properties of Nd0.7Ca0.3MnO3 Nanomanganite

Nanoscale materials show different properties compared to bulk materials. Due to the size dependent properties the nanoscale materials have potential applications in industry. In this paper the size dependent magnetic properties of Nd0.7Ca0.3MnO3 nanomanganite have been investigated. Nd0.7Ca0.3MnO3 nanoparticles were prepared by low temperature sol-gel method. X-ray diffraction (XRD), Transmission Electron Microscopy (TEM) and EDAX techniques were used to understand the structure, grain size and composition. Nanoparticles prepared were of the sizes 15 nm, 19 nm and 25 nm respectively. SQUID magnetometer was used to study the magnetic behavior of the nanoparticles. Field cooled (FC) and zero field cooled (ZFC) magnetization of all the nanosamples with respect to temperature was studied and compared. We have observed drastic changes in magnetic properties of 15 nm particles compared to the other nanoparticles. The `charge order peak' was seen to have disappeared in 15 nm particles while it was present in the other nanoparticles. All the nano particles exhibit superparamagnetism whose blocking temperature decreases as a function of decreasing particle size. The possible reasons for the influence of the particle size on the magnetic properties are discussed.

Phenomenology and control of buckling dynamics in multicomponent colloidal droplets

Self-assembly of nano sized particles during natural drying causes agglomeration and shell formation at the surface of micron sized droplets. The shell undergoes sol-gel transition leading to buckling at the weakest point on the surface and produces different types of structures. Manipulation of the buckling rate with inclusion of surfactant (sodium dodecyl sulphate, SDS) and salt (anilinium hydrochloride, AHC) to the nano-sized particle dispersion (nanosilica) is reported here in an acoustically levitated single droplet. Buckling in levitated droplets is a cumulative, complicated function of acoustic streaming, chemistry, agglomeration rate, porosity, radius of curvature, and elastic energy of shell. We put forward our hypothesis on how buckling occurs and can be suppressed during natural drying of the droplets. Global precipitation of aggregates due to slow drying of surfactant-added droplets (no added salts) enhances the rigidity of the shell formed and hence reduces the buckling probability of the shell. On the contrary, adsorption of SDS aggregates on salt ions facilitates the buckling phenomenon with an addition of minute concentration of the aniline salt to the dispersion. Variation in the concentration of the added particles (SDS/AHC) also leads to starkly different morphologies and transient behaviour of buckling (buckling modes like paraboloid, ellipsoid, and buckling rates). Tuning of the buckling rate causes a transition in the final morphology from ring and bowl shapes to cocoon type of structure. (C) 2015 AIP Publishing LLC.

Temperature-Dependent Magnetic and EPR Studies of Bulk and Nanoparticles of Bi0.1Ca0.9MnO3

We report temperature-dependent magnetic and electron paramagnetic resonance (EPR) properties of bulk and nanoparticle samples of Bi0.1Ca0.9MnO3 (BCMO). The nanoparticles of BCMO (dia similar to 50 nm) were prepared by the standard sol-gel technique and bulk samples by solid-state reaction method. We have investigated the magnetic ordering in the two samples by carrying out temperature-dependent magnetic and EPR studies and compared their properties. According to earlier reports, antiferromagnetic and ferromagnetic orders coexist in the bulk sample of Bi0.1Ca0.9MnO3. Our magnetization and EPR results show the existence of ferromagnetism in the bulk sample which is present in the nanosample as well but with somewhat weakened strength with the size reduction.

Synthesis and characterization of magnetic and conductive nickel ferrite-polyaniline nanocomposites

Conducting polymer/ferrite nanocomposites with an organized structure provide a new functional hybrid between organic and inorganic materials. The most popular among the conductive polymers is the polyaniline due to its wide application in different fields. In the present work nickel ferrite nanoparticles were prepared by sol-gel citrate-nitrate method. Polyaniline/nickel ferrite nanocomposites were synthesized by a simple general and inexpensive in-situ polymerization in the presence of nickel ferrite nanoparticles. The effects of nickel ferrite nanoparticles on the DC-electrical and magnetic properties of polyaniline were investigated. The structural, morphological and thermal stability of nanocomposites were characterized by X-ray diffraction, FTIR, scanning electron micrograph and TGA. The DC conductivity of polyaniline/nickel ferrite nanocomposites have been measured as a function of temperature in the range of 80K to 300K. The magnetic properties of the nanocomposites were measured using vibrating sample magnetometer in the temperature range 300-10K up to 30 kOe magnetic field.

Electron Magnetic Resonance Studies of Nanosized Nd0.65Ca0.35 Mn1-xCrxO3 (x=0, 0.06, 0.1) Manganite

We report a systematic investigation of the temperature dependence of electron magnetic resonance (EMR) line width, intensity and resonance field for similar to 25 nm Nd0.65Ca0.35MnO3 (NCMO1), Nd0.65Ca0.35Mn0.94Cr0.06O3 (NCMO2) and Nd0.65Ca0.35Mn0.9Cr0.1O3 (NCMO3) nanoparticles prepared by sol-gel method. The EMR line widths for the three nano-samples differ significantly from one another below a temperature T (min) where the line width has a minimum. T (min) was found to be 130, 100 and 120 K for NCMO1, NCMO2 and NCMO3, respectively. Well above T (min) the line width values for the three samples are close to one another. The sharp upturn of EMR line width below T (min) is attributed to the formation of short range, ferromagnetically ordered clusters. Temperature dependence of EMR intensity shows a residual CO transition in NCMO1 and NCMO2 and a complete disappearance of it in NCMO3. The intensity undergoes significant increase below 120, 80 and 100 K for NCMO1, NCMO2 and NCMO3, respectively, indicating the onset of ferromagnetic transitions. The occurrence of ferromagnetic transition is further confirmed by magnetization hysteresis measurements. The decrease in T (C) in NCMO2 and NCMO3 compared to NCMO1 nanoparticles is understood to be due to the destruction of the double-exchange interaction by chromium doping. The resonance field decreases below the ferromagnetic onset temperatures for all the samples as expected. The combined effects of the reduction in size and of chromium doping in Mn site are discussed.

Structural modification and enhanced magnetic properties with two phonon modes in Ca-Co codoped BiFeO3 nanoparticles

Bi1-xCaxFe1-xCoxO3 nanoparticles with x=0.0, 0.05, 0.10 and 0.15 were successfully synthesized by cost effective tartaric acid based sol gel route. The alkali earth metal Ca2+ ions and transition metal Co3+ ions codoping at A and B-sites of BiFeO3 results in structural distortion and phase transformation. Rietveld refinement of XRD patterns suggested the coexistence of rhombohedral and orthorhombic phases in codoped BiFeO3 samples. Both XRD and Raman scattering studies showed the compressive lattice distortion in the samples induced by codoping of Ca2+ and Co3+ ions. Two-phonon Raman spectra exhibited the improvement of magnetization in these samples. X-ray photoelectron spectroscopy (XPS) showed the dominancy of Fe3+ and Co3+ oxidation states along with the shifting of the binding energy of Bi 4f orbital which confirms the substitution Ca2+ at Bi-site. The magnetic study showed the enhancement in room temperature ferromagnetic behavior with co-substitution consistent with Rama analysis. The gradual change in line shape of electron spin resonance spectra indicated the local distortion induced by codoping. (C) 2015 Published by Elsevier Ltd and Techna Group S.r.l.

Surface modification of titania aerogel films by oxygen plasma treatment for enhanced dye adsorption

Titania aerogels were synthesized by sol-gel route followed by ambient pressure subcritical drying technique. The aerogels synthesized in the present work possess a maximum surface area of 252 m(2)/g. The pore size distribution is between 2 and 30 nm which confirms their mesoporosity. The oxygen plasma treatment on titania aerogel thin films improved the surface area up to 273 m(2)/g and produced additional hydrophilic groups on the surface. It is confirmed by BET surface area, XPS and thermal analysis in conjunction with dye adsorption studies. After plasma treatment the dye adsorption capacity was increased 2.5 times higher than that of untreated aerogel film. The increased surface area and the hydrophilic groups generated on the titania aerogel surface during plasma treatment are responsible for enhanced dye adsorption. The overall nanoporous morphology of titania aerogel is preserved after plasma treatment. (C) 2015 Elsevier B.V. All rights reserved.